Index: src/OFMutableSet.h
==================================================================
--- src/OFMutableSet.h
+++ src/OFMutableSet.h
@@ -50,6 +50,13 @@
  *	  set.
  *
  * \param set The set to intersect
  */
 - (void)intersectSet: (OFSet*)set;
+
+/**
+ * \brief Creates a union of the receiver and the specified set.
+ *
+ * \param set The set to create the union with
+ */
+- (void)unionSet: (OFSet*)set;
 @end

Index: src/OFMutableSet.m
==================================================================
--- src/OFMutableSet.m
+++ src/OFMutableSet.m
@@ -63,10 +63,22 @@
 
 	for (i = 0; i < count; i++)
 		if (![set containsObject: cArray[i]])
 			[self removeObject: cArray[i]];
 
+	[pool release];
+}
+
+- (void)unionSet: (OFSet*)set
+{
+	OFAutoreleasePool *pool = [[OFAutoreleasePool alloc] init];
+	OFEnumerator *enumerator = [set objectEnumerator];
+	id object;
+
+	while ((object = [enumerator nextObject]) != nil)
+		[self addObject: object];
+
 	[pool release];
 }
 
 - (int)countByEnumeratingWithState: (of_fast_enumeration_state_t*)state
 			   objects: (id*)objects

Index: tests/OFSet.m
==================================================================
--- tests/OFSet.m
+++ tests/OFSet.m
@@ -84,12 +84,14 @@
 	TEST(@"-[intersectSet:]",
 	    R([mutableSet intersectSet: ([OFSet setWithObjects: @"baz",
 	    nil])]) && [mutableSet isEqual: ([OFSet setWithObjects: @"baz",
 	    nil])])
 
-	[mutableSet addObject: @"baz"];
-	[mutableSet addObject: @"x"];
+	TEST(@"-[unionSet:]",
+	    R([mutableSet unionSet: ([OFSet setWithObjects: @"x", @"bar",
+	    nil])]) && [mutableSet isEqual: ([OFSet setWithObjects: @"baz",
+	    @"bar", @"x", nil])])
 
 #ifdef OF_HAVE_FAST_ENUMERATION
 	ok = YES;
 	i = 0;